RS‐485 Notes

AquaLogic/ProLogic uses an RS-485 half-duplex bus running at 19200 baud (no parity, 8 data bits, 2 stop bits) to communicate with remotes, pumps, etc. Note the main control panel also sits on this bus (and is identical to the wired remotes aside from the color and extra buttons; the system works fine without one plugged in).

Pinouts on the control panel and the remotes are as follows:

Red    -> +10V
Black  -> A
Yellow -> B
Green  -> Ground

An RS-485 bus either requires a master, or some form of collision detection. The Goldline Aqua Connect manual states:

The Aqua Logic PS/Pro Logic PS is the master of the bus, and devices only transmit when queried. For example, to receive a keypress from any one of the remote controls, the Aqua Logic PS/Pro Logic PS requests pending keys every 100 ms, and then listens for an answer. If any remote control has a pending keypress, it is immediately sent back to the Aqua Logic PS/Pro Logic PS.

A logic trace of the RS-485 bus shows that when a key is pressed the remote sends the response less than 1ms after the keep-alive packet.

Without a dedicated piece of hardware controlling the timing, all the code can do is wait for the keep-alive packet and then blast out the response. This seems to work most of the time, but is obviously at the mercy of network congestion, OS scheduling, etc. etc.